Spectroscopic study of water adsorption on Li(+), TMA(+) and HDTMA(+) exchanged montmorillonite.

The potential of IR and NMR spectroscopy in characterization the interaction of water with natural and organically modified montmorillonites was introduced. Organoclays were prepared from Li-saturated montmorillonite (Li-S) and tetramethylammonium (TMA) or hexadecyltrimethylammonium (HDTMA) salts. The influence of organic cation size on the water vapour uptake was examined and a comparative study with natural clay mineral was provided. The near-IR spectra confirmed the reduced water content in TMA-S and HDTMA-S. After exposure of the samples to water vapour under various relative humidities (RH) the H2O content was determined. According to the adsorption isotherms the amount of water decreased in order Li-S>TMA-S>HDTMA-S. The intensities of the 2νOH and [Formula: see text] bands, corresponding to the vibrations of H2O, gradually increased in hydrated samples. The (13)C MAS NMR and near-IR of hydrated organoclays confirmed the presence of H2O close to the cation's headgroup. NMR signals of inner -CH2- groups in HDTMA-S were also affected by hydration: the intensity of disordered gauche conformers (31.1 ppm) overtook the intensity of ordered all-trans conformers (33.0 ppm).